Effects Of Transplanting Period On Growth And Development Of Flue-cured Tobacco And Usability Of Upper Tobacco Leaves

In order to explore the suitable transplanting period of the enriched flavour flue-Cured tobacco in Xintian County,Yongzhou City,Yunyan 87 was used as experimental material to study the effects of different transplanting periods on the growth and development of flue-cured tobacco and the usability of upper tobacco leaves.The experiment was carried out in Xinxu tobacco leaf base of Xintian County,Yongzhou City,Hunan Province from2017 to 2018.The changes of growth period of flue-cured tobacco at different transplanting stages and the climatic factors,agronomic characters,photosynthetic characteristics,chemical indexes,chemical composition coordination and economic characteristics of tobacco at different growth stages were analyzed,and the main factors were treated at different transplanting stages by using fuzzy mathematics and weighting method.The economic effect index（ECI）and chemical composition availability index（CCUI）of grade I tobacco leaves were evaluated to determine the economic effect and availability of tobacco leaves.The effects of climate and environmental conditions caused by different transplanting time on the growth and development of flue-cured tobacco and the quality of tobacco leaves were discussed comprehensively.The results are as follows:（1）The growth period of tobacco plant was postponed with the postponement of transplanting period,and the whole growth period of field was shortened obviously.The whole growth period was shortened successively when transplanting period was delayed for5 days,and the shortening of transplanting time was the most obvious.Appropriate postponement of transplanting can make tobacco plants avoid the environment of rainy and low temperature in the early stage,which is conducive to early growth and rapid development of tobacco plants.（2）Different transplanting stages will lead to different temperature and precipitation conditions in different growth stages of tobacco plants.The precipitation of the experimental plot changed regularly with the postponement of transplanting period.The precipitation of the field decreased in turn with the postponement of transplanting period.The difference of precipitation in root extension period was the most obvious.The precipitation of T2 and T3treatment was more suitable,and the difference of precipitation between booming period and mature period was smaller.The temperature of each growth period increased gradually with the transplanting period,but the accumulated temperature of field activities had little difference.（3）With the postponement of transplanting period,the plant height and pitch of tobacco plants showed an increasing trend on the whole,and the leaf area showed a trend of first increasing and then decreasing,while the stem circumference did not show regular changes.The length and width of upper leaves increased rapidly in 0-30 days,especially in the previous 20 days.After 30 days,the growth rate was slow and the trend was gentle.The average growth rate of leaf length and width of upper leaves of tobacco plants under T3treatment（delayed transplanting for 5 days）was higher than that of other treatments at 0-20days and 0-50 days of leaf age.The growth rate of upper leaves was faster and the opening of leaves was the most obvious.（4）Transplanting period had a significant effect on Photosynthetic Characteristics of upper,middle and lower leaves.Net photosynthetic rate and stomatal conductance decreased with the postponement of transplanting period,while intercellular CO₂ concentration increased.The diurnal variation of net photosynthetic rate and stomatal conductance of upper tobacco leaves showed a bimodal curve,with peaks at 9:00-11:00 and 13:00-15:00,respectively.The intercellular CO₂ concentration of upper tobacco leaves showed a sharp decline in the morning,a gentle trend in the afternoon and an upward trend in the evening.（5）With the postponement of transplanting period,nicotine in upper leaves showed a downward trend,while total sugar and reducing sugar showed an upward trend.The main chemical composition indexes of upper tobacco leaves were in the suitable range,and the nicotine content was the highest in T1 treatment,which was significantly higher than other treatments;the total sugar and reducing sugar content was the best in T2 and T3 treatment,which was in the suitable range of high-quality tobacco leaves;the sugar-base ratio and nitrogen-base ratio were generally low,and the K-chlorine ratio was appropriate.Among the four treatments,the chemical availability index（CCUI）reached 73.34 and 70.08 in T2treatment in 2017 and 2018,and showed a"low-high-low"variation with the postponement of transplanting period.（6）The economic traits of flue-cured tobacco showed obvious differences with the change of transplanting.The yield,output value,the proportion of top-grade tobacco leaves and the proportion of middle-grade tobacco leaves in T2 treatment were the best,followed by CK treatment,and the economic traits were better than other treatments as a whole.The economic effect index（ECI）increased first and then decreased with the postponement of transplanting period.